University of Wollongong Research Online University of Wollongong Thesis Collection 1954-2016 University of Wollongong Thesis Collections 2008 Interleaved spread spectrum orthogonal frequency division multiplexing for system coexistence Pingzhou Tu University of Wollongong Recommended Citation Tu, Pingzhou, Interleaved spread spectrum orthogonal frequency division multiplexing for system coexistence, PhD thesis, School of Electrical, Computer and Telecommunication Engineering, University of Wollongong, 2008. http://ro.uow.edu.au/theses/349 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: research-pubs@uow.edu.au
Interleaved Spread Spectrum Orthogonal Frequency Division Multiplexing for System Coexistence Pingzhou Tu A thesis submitted for the degree Doctor of Philosophy University of Wollongong School of Electrical, Computer and Telecommunication Engineering July 2008
ii Abstract Various kinds of wireless communication devices and systems provide a number of different functions and services to meet different demands for people. Some of these devices and systems coexist in the same area and share the common frequency bands according to some coexistence mechanisms such as cooperative and non-cooperative mechanisms. These mechanisms including power control, frequency hopping and time division multiplexing technique can handle electromagnetic interference between coexistence devices to some extent, but for the coexistence systems the interference problems between these systems are still very serious issues which affect coexistence system performance. In this thesis we consider the system coexistence interference problems in the spectrum shared environments. Rather than applying the techniques of power control, frequency control, time control and spatial control to avoid interference, we attempt to address the fundamental nature of system transmission. The general philosophy is to combine the orthogonal frequency division multiplexing (OFDM) technique with a spectrum spread method to generate an interleaved spectrum spread OFDM (ISS-OFDM) multiple subband signal, so that the system transmission subbands are selected adaptively and system coexistence interference is avoided and suppressed. This approach reveals the potential ability of system coexistence. Simulated results on system performance such as peak to average power ratio (PAR), signal frequency diversity and time diversity, and system bit error rate (BER) are presented to verify that system transmission bandwidth can be adaptively selected to avoid interference of coexistence systems and improve system performance. We then consider the implications of choosing or dropping the subbands with different levels of interference from the multiple subbands of the ISS-OFDM signal, and show that (i) it is possible to implement the information transmission without
iii information loss by selecting some of the subbands with an interference level below the threshold, and dropping the subbands with an interference level over the threshold, and (ii) it is possible to derive the interference thresholds, based on which the adaptive selection subband transmission is implemented. We also show that it is possible to replace the interference thresholds over multipath fading channels by the interference thresholds over the Gaussian channels, so that the derivation process of interference thresholds over the multipath fading channels is greatly simplified. Through the theoretical analysis and investigations, we show that the ISS-OFDM technique can be applied to the coexisting systems sharing the frequency bands in the industrial, scientific and medical (ISM) band. Coupled with a technique for cognitive radios, the ISS-OFDM can be applied to a wide class of problems covering the interference suppression and spectrum efficiency improvement.
iv Declaration This is to certify that the work presented in this thesis is solely my own, except where due reference is made in the text. No work in this thesis has been submitted for degree to any other university or institutions. Signed Pingzhou Tu July 18, 2008
v Acknowledgements The work presented in this thesis would not have been possible without the help and the support of the following people. My supervisor Associate Professor Xiaojing Huang, with his guidance, insight, enthusiasm and unique wit, has inspired me to advance towards the Ph.D goals step by step. My co-supervisor Professor Eryk Dutkiewicz, with his many helpful suggestions on this work and his generous financial support, has made me concentrate on my Ph.D study without any disturbance. My wife, Gang Xu, and my two lovely sons, Robert Tu and Michael Tu, have encouraged and pushed me to work very hard toward my career destination. My fellow students in the Wireless Technologies Laboratory and ICT Research Institute and stuff of the School provided me with a lot of advice and help in my daily research work.
vi Contents Chapter 1 Introduction...1 1.1 Wireless Coexistence Environment...1 1.2 Coexistence Modes...2 1.3 Advantages of System Coexistence...7 1.4 Coexistence Problems...7 1.5 Interference Sources...8 1.6 Existing Solutions...11 1.7 Solutions in This Thesis...15 1.8 Objectives and Overview of This Thesis...15 1.9 Publications...17 1.10 Contributions...19 Chapter 2 Literature Review...21 2.1 Introduction...21 2.2 Example 1: Erasure of OFDM Subcarriers...22 2.2.1 Scenario...22 2.2.2 Problems...23 2.2.3 Solutions...25 2.3 Example 2: Reactive Coordination Method...26 2.3.1 Scenario...26
vii 2.3.2 Problems...27 2.3.3 Solutions...28 2.3.4 Summary...29 2.4 VISA: A Solution Using Spatial Resource...30 2.5 System Coexistence Using Cognitive Radio Techniques...31 2.5.1 Problems...31 2.5.2 Proposed Methods...32 2.6 Summary...35 Chapter 3 Theory of Baseband Signal Processing...36 3.1 Introduction...36 3.2 Spectrum Spreading Techniques...36 3.2.1 Direct Sequence Spread Spectrum...38 3.2.2 Frequency Hopping Spread Spectrum...44 3.3 Methods of Random Signal Processing...46 3.3.1 Random Variables, Probability Distributions and Densities...46 3.3.2 Gaussian Distributions...47 3.3.3 Error Probability of Binary Modulation...47 3.4 OFDM Techniques...51 3.4.1 Multicarrier Transmission...51 3.4.2 Multicarrier Transmission Characteristics...52 3.4.3 OFDM Techniques...54 3.5 Channel Statistical Characteristics...55 3.6 Summary...58 Chapter 4 Multiple Subband Signal...60 4.1 Introduction...60
viii 4.2 System Architecture...68 4.3 Transmitter Architecture...71 4.3.1 QPSK Mapping...72 4.3.2 Serial/Parallel Converter and Modified OFDM Modulation...74 4.4 Interleaving...76 4.4.1 Pseudorandom Interleaving...76 4.4.2 Convolution Interleaving...77 4.4.3 Odd-Even Symmetric Interleaver...78 4.4.4 Periodical Interleaving...79 4.5 Generation of ISS-OFDM Symbol...80 4.6 Cyclic Prefix and ISI...83 4.6.1 Cyclic Prefix Insertion...83 4.6.2 Pulse Shaping...85 4.7 Multiple Subband Signal...88 4.8 Summary...89 Chapter 5 Channel Characterization...91 5.1 Introduction...91 5.2 AWGN Channel...92 5.3 Fading Channel...93 5.3.1 Statistical Characteristics...93 5.3.2 Channel Models...95 5.3.3 Frequency Non-Selective Fading Channels...96 5.3.4 Frequency Selective Channels...97 5.4 Faded Multiple Subband Signal...98 5.5 Interference...100
ix 5.6 Summary...101 Chapter 6 Reception of Multiple Subband Signal...103 6.1 Introduction...103 6.2 Receiver Signal Filtering...104 6.3 Cyclic Prefix Removal...106 6.4 Deinterleaver...107 6.5 Solution I: Serial Demodulation Using One FFT...109 6.5.1 Receiver Structure of Serial Demodulation...110 6.5.2 Demodulation...110 6.5.3 Channel Compensation...112 6.6 Solution II: Reception Using Parallel FFTs...118 6.6.1 Receiver Input Signal...118 6.6.2 Parallel Demodulation FFTs...119 6.6.3 MRC Equalization...121 6.7 Summary...122 Chapter 7 Performance Analysis...124 7.1 Peak to Average Power Ratio...124 7.1.1 Introduction...124 7.1.2 PAR Calculation...126 7.1.3 Phase Shifting and Interleaving...127 7.1.4 PAR Comparison...128 7.1.5 PAR Simulation and Analysis...129 7.1.6 PAR Improvement...132 7.2 Diversity Performance...132 7.2.1 Introduction...132
x 7.2.2 Diversity in ISS-OFDM signals...134 7.2.3 Scalability of Diversity...134 7.2.4 Summary...136 7.3 System Coexistence Performance...136 7.3.1 Introduction...136 7.3.2 Adaptive Subband Selection...137 7.4 Filtering of Multiple Subband Signal...143 7.5 System Performance...1444 7.6 Summary...146 Chapter 8 Contribution and Future Work...147 8.1 Contribution...147 8.2 Applications...149 8.3 Future Work...150
xi List of Figures Figure 1.1 Review of systems coexistence...5 Figure 1.2 Frequency range for wireless electromagnetic channels...10 Figure 1.3 Framework of the whole thesis....17 Figure 2.1 Coexistence between Bluetooth and Wi-Fi...23 Figure 2.2 (a) Coexistence interference between IEEE 802.15.1a and IEEE 802.11g in frequency domain; (b) Coexistence interference between IEEE802.15.1a and IEEE 802.11g in the time domain...24 Figure 2.3 Erasure of interference signal from Bluetooth in the Wi-Fi band...25 Figure 2.4 Coexistence between IEEE 802.11b and IEEE 802.16a....26 Figure 2.5 Spectrum allocations between IEEE 802.116a and IEEE 802.11b....27 Figure 2.6 Architecture of cognitive radio....34 Figure 3.1 Direct sequence spread spectrum system model...39 Figure 3.2 Frequency hopping spread spectrum system model...45 Figure 3.3 PDF and CDF...47 Figure 3.4 Theory of baseband signal processing....59 Figure 4.1 OFDM system model....62 Figure 4.2 OFDM modulation and demodulation....63 Figure 4.3 Baseband system model....70 Figure 4.4 Transmitter model....72 Figure 4.5 (a) Mapping of QPSK; (b) Relation between QPSK and BPSK...73 Figure 4.6 Convolutional interleaving with register number M = 4 and symbol storage J = 1...78 Figure 4.7 Periodical interleaving...79 Figure 4.8 Modulation and interleaving process with subcarrier number N = 4....81 Figure 4.9 Spectrum of ISS-OFDM symbol with subcarrier number N = 4...83
xii Figure 4.10 Cyclic prefix insertion...85 Figure 4.11 Impulse response of the adaptive filter with a breakpoint....86 Figure 4.12 Pulse shaping signal....87 Figure 4.13 Spectrum of ISS-OFDM signal...88 Figure 4.14 Transmitted ISS-OFDM signal in one symbol with N = 8 in the time domain....89 Figure 5.1 Propagation channel model for AWGN noise...93 Figure 5.2 Multiple subband signal after Rayleigh fading....99 Figure 5.3 Channel fading effects on subbands when subcarrier number N = 4...99 Figure 6.1 (a) Filter impulse responses with different subband configurations; (b) Filter passbands with different subband configurations....105 Figure 6.2 Adaptive filtering at receiver...106 Figure 6.3 Cyclic prefix removal...107 Figure 6.4 The principle of deinterleaver....108 Figure 6.5 Implementation of periodical deinterleaver....109 Figure 6.6 Serial demodulation and equalization....110 Figure 6.7 Frequency domain equalizer....113 Figure 6.8 The structure of R( k )....114 Figure 6.9 SNR normalization...117 Figure 6.10 Parallel demodulation and combination...119 Figure 7.1 Transmitted signals waveforms with different spreading factors....131 Figure 7.2 PAR performance for ISS-OFDM signals with different number of subbands...131 Figure 7.3 Bandwidth reconfigurable system and efficient spectrum usage...135 Figure 7.4 Subband selection by using adaptive filter...139 Figure 7.5 INR thresholds over multipath fading channel....142 Figure 7.6 BER performance without interferences in fading channel....145 Figure 7.7 BER performance with interferences in fading channel....145 Figure 7.8 BER performance after interfered subbands removed adaptively in the fading channels....146
xiii List of Tables Table 7.1 Threshold comparison between Gaussian and multipath channels at Eb / N = 10dB..143 0
xiv List of Abbreviations AFD-OFDM adaptive frequency diversity OFDM AP access point AWGN additive white Gaussian channel BER bit error rate BPSK binary phase shift keying BS base station CDMA code division multiple access CES complex exponential spreading CI convolutional interleaving CR cognitive radios CSMA/CA carrier sense multiple access/collision avoidance CTS clear to send CP cyclic prefix CDF cumulative distribution function DAB digital audio broadcast DFS dynamic frequency selection DSSS direct sequence spread spectrum FDD frequency division duplex FDMA frequency diversion multiple access FFT fast Fourier transform MWT modified Walsh transform FH frequency hopping FH-SS frequency hopped spread spectrum FSK frequency shift keying FD-OFDM frequency diversity OFDM GFSK Gaussian frequency shift keying ICI inter channel interference IFFT inverse fast Fourier transform
xv ISI inter symbol interference ISM industrial, scientific and medical ISS-OFDM interleaved spread spectrum orthogonal frequency division multiplexing LOS line-of-sight MAC medium access control MB-OFDM multiband OFDM MBOA multiband OFDM alliance MBOA-UWB MBOA ultra-wideband MIMO-OFDM multiple-input multiple-output OFDM MRC maximum ratio combining MC-CDMA multicarrier CDMA OESI odd-even symmetric interleaver OFDM orthogonal frequency division multiplexing PAM pulse amplitude modulation PAR peak-to-average power ratio PC power control PCB printed circuit board PDA personal digital assistant PDF probability density function PI periodic interleaving QAM quadrature amplitude modulation QPSK quadrature phase shift keying RF radio frequency RTS request to send RS Reed-Solomon RSSI received signal strength indicator SDMA spatial division multiple access SDR software designed radio SI spread interleaving SINR signal to interference noise ratio SIR signal to interference ratio SS subscriber station
xvi SS-MC-MA SS-OFDM TA TDD TDMA UHF UWB VHF VISA VoIP WBAN WiMAX Wi-Fi WLAN WMAN WPAN spread-spectrum multiple-carrier multiple-access spread spectrum OFDM time agility time division duplex time division multiple access ultra high frequency ultra-wideband very high frequency virtual subcarrier assignment voice over Internet protocol wireless body area networks worldwide interoperability for microwave access wireless fidelity wireless local area networks wireless metropolitan area network wireless personal area network